The Radiation Monitoring Devices (RMD) demonstrated in Phase I of this contract that the photovoltaic CdTe radiation sensor had suitable performance characteristics for use in an automatic exposure controller. In Phase II, the detector research will be completed, the hardware and software developed and fully operational prototype system constructed for testing with clinical phantoms in collaboration with their medical and industrial consultants. The specific aims of Phase II are: 1. Establish improved crystal growth techniques for producing photovoltaic CdTe detectors with reproducible characteristics representative of the best detectors developed in Phase I. 2. Conduct further research on better detector fabrication procedures to enhance sensitivity, speed of response and noise characteristics. 3. Develop the hardware and software needed to implement this concept into an all solid state, x-ray exposure controller. 4. Design and build a full scale, portable laboratory prototype capable of being used at the facilities of our collaborators. 5. Conduct extensive tests of the prototype system to ensure optimum performance, reliability and ease of use under all relevant conditions. Finally, the controller will be designed to become part of the new General Electric mammography machine now being developed by RMD collaborator LoRad Corporation.